Low-manganese gas-shielded flux cored welding electrodes

ABSTRACT

A gas-shielded flux cored welding electrode comprises a ferrous metal sheath and a core within the sheath enclosing core ingredients. The core ingredients and sheath together comprise, in weight percentages based on the total weight of the core ingredients and the sheath: 0.25 to 1.50 manganese; 0.02 to 0.12 carbon; 0.003 to 0.02 boron; 0.2 to 1.5 silicon; 0 to 0.3 molybdenum; at least one of titanium, magnesium, and aluminum, wherein the total content of titanium, magnesium, and aluminum is 0.2 to 2.5; 3 to 12 titanium dioxide; at least one arc stabilizer, where the total content of arc stabilizers is 0.05 to 1.0; no greater than 10 of additional flux system components; remainder iron and incidental impurities.

FIELD OF THE DISCLOSURE

The disclosure relates generally to gas-shielded flux cored arc weldingelectrodes, and more particularly to gas-shielded flux cored arc weldingelectrodes having low manganese content.

BACKGROUND OF THE DISCLOSURE

The American Welding Society specifications AWS A5.20/A5.20M and AWSA5.36/A5.36M, and other similar global specifications, govern thetechnical requirements for flux cored electrodes designed for weldingcarbon steels. For gas-shielded flux cored carbon steel electrodesclassified as E7XT-1C, E7XT-1M, E7XT-9C, E7XT-9M, E7XT-12C, and E7XT-12Mand containing titanium dioxide (TiO₂) based slag systems, AWSA5.20/A5.20M and AWS A5.36/A5.36M require the alloy content in the weldmetal to be no greater than 1.75% manganese (1.60% for E7XT-12 type),0.12% carbon, 0.90% silicon, 0.20% chromium, 0.50% nickel, 0.30%molybdenum, 0.08% vanadium, and 0.35% copper Although nickel isbeneficial to weld metal toughness and ductility properties, the maximumallowed nickel level in these electrode types is fairly restrictive.Therefore, carbon, manganese, molybdenum, and silicon levels typicallyare adjusted to optimize weld metal properties.

In general, conventional gas-shielded flux cored welding electrodes withtitanium dioxide based slag systems include significant levels ofmanganese and also may include small concentrations of boron to achievedesired weld metal toughness, tensile, and ductility properties. Adrawback of conventional gas-shielded flux cored electrodes includingtitanium dioxide based slag systems is that the significant manganeselevels that these electrodes contain may not meet certain emissionscontrol regulations. For example, Metal Fabrication Hazardous AirPollutants (MFHAP) requirements under U.S. Environmental ProtectionAgency regulations at 40 CFR Part 63 Subpart XXXXXX, which recentlybecame effective, limit the manganese content of certain weldingelectrodes to less than 1.0 weight percent, based on total electrodeweight.

The objectives of the present disclosure are to provide a gas-shieldedflux cored electrode with a titanium dioxide based slag system thatcontains relatively low manganese content and produces welding fumescontaining relatively low manganese levels, but produces weld depositshaving mechanical properties that meet certain applicable requirements.

SUMMARY

The present disclosure provides a gas-shielded flux cored weldingelectrode comprising a ferrous metal sheath and a core within thesheath. The core and sheath together comprise, in weight percentagesbased on the total weight of the core and sheath: 0.25 to 1.50manganese; 0.02 to 0.12 carbon; 0.003 to 0.02 boron; 0.2 to 1.5 silicon;0 to 0.3 molybdenum; at least one of titanium, magnesium, and aluminum,wherein the total content of titanium, magnesium, and aluminum is 0.2 to2.5; 3 to 12 titanium dioxide; at least one arc stabilizer, where thetotal content of arc stabilizers is 0.05 to 1.0; no greater than 10 ofadditional flux system components; remainder iron and incidentalimpurities. The welding electrode includes significantly less manganesethan certain conventional commercially available gas-shielded flux coredwelding electrodes, yet may be formulated to provide tensile and otherproperties similar to conventional electrodes including substantiallyhigher manganese content.

The reader will appreciate the foregoing details and advantages of thepresent invention, as well as others, upon considering the followingdetailed description of certain non-limiting embodiments of theinvention. The reader also may comprehend such additional details andadvantages of the present invention upon making and/or using embodimentswithin the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, specific embodiments of the disclosed device will nowbe described, with reference to the accompanying drawings, in which:

FIG. 1 is a graph plotting the weight percentage manganese in weldingfumes as a function of manganese concentration in a 1/16-inch diameterE71T-9M flux cored welding electrode during gas-shielded arc weldingusing a 75% Ar/25% CO₂ shielding gas.

FIG. 2 is a graph plotting the weight percentage manganese in welddeposits as a function of welding electrode manganese concentration whenthe deposits were formed using a 1/16-inch diameter E71T-9M flux coredwelding electrode and gas-shielded arc welding using a 75% Ar/25% CO₂shielding gas.

FIG. 3 is a graph plotting yield strength (YS) and ultimate tensilestrength (UTS) of weld deposits as a function of welding electrodemanganese concentration when the deposits were formed using a 1/16-inchdiameter E71T-9M flux cored welding electrode and gas-shielded arcwelding using a 75% Ar/25% CO₂ shielding gas.

FIG. 4 is a graph plotting Charpy v-notch (CVN) impact toughness(evaluated at −20° F.) of weld deposits as a function of weldingelectrode manganese content when the deposits were formed using a1/16-inch diameter E71T-9M flux cored welding electrode and gas-shieldedarc welding using a 75% Ar/25% CO₂ shielding gas.

FIG. 5 is a graph plotting fume generation rate (FGR) as a function ofwelding electrode manganese content when the deposits were formed usinga 1/16-inch diameter E71T-9M flux cored welding electrode andgas-shielded arc welding using a 75% Ar/25% CO₂ shielding gas.

DETAILED DESCRIPTION

Various welding electrode embodiments are described in thisspecification to provide an overall understanding of the invention. Itis understood that the various embodiments described in thisspecification are non-limiting and non-exhaustive. Thus, the inventionis not limited by the description of the various non-limiting andnon-exhaustive embodiments disclosed in this specification. Inappropriate circumstances, the features and characteristics described inconnection with various embodiments may be combined with the featuresand characteristics of other embodiments. Such modifications andvariations are intended to be included within the scope of thisspecification. As such, the claims may be amended to recite any steps,elements, limitations, features, and/or characteristics expressly orinherently described in, or otherwise expressly or inherently supportedby, this specification. Further, Applicants reserve the right to amendthe claims to affirmatively disclaim steps, elements, limitations,features, and/or characteristics that are present in the prior artregardless of whether such features are explicitly described herein.Therefore, any such amendments comply with the requirements of 35 U.S.C.§ 112, first paragraph, and 35 U.S.C. § 132(a). The various embodimentsdisclosed and described in this specification can comprise, consist of,and/or consist essentially of the elements, limitations, features,and/or characteristics as variously described herein.

Any patent, publication, or other disclosure material identified hereinis incorporated by reference into this specification in its entiretyunless otherwise indicated, but only to the extent that the incorporatedmaterial does not conflict with existing definitions, statements, orother disclosure material expressly set forth in this specification. Assuch, and to the extent necessary, the express disclosure as set forthin this specification supersedes any conflicting material incorporatedby reference herein. Any material, or portion thereof, that is said tobe incorporated by reference into this specification, but whichconflicts with existing definitions, statements, or other disclosurematerial set forth herein, is only incorporated to the extent that noconflict arises between that incorporated material and the existingdisclosure material. Applicants reserve the right to amend thisspecification to expressly recite any subject matter, or portionthereof, incorporated by reference herein.

The grammatical articles “one”, “a”, “an”, and “the”, if and as used inthis specification, are intended to include “at least one” or “one ormore”, unless otherwise indicated. Thus, the articles are used in thisspecification to refer to one or more than one (i.e., to “at least one”)of the grammatical objects of the article. By way of example, “acomponent” means one or more components, and thus, possibly, more thanone component is contemplated and may be employed or used in animplementation of the described embodiments. Further, the use of asingular noun includes the plural, and the use of a plural noun includesthe singular, unless the context of the usage requires otherwise.

Various embodiments described herein are directed to gas-shielded fluxcored welding electrodes including titanium dioxide based slag systemsand relatively low manganese content. The relatively low manganesecontent in embodiments of flux cored welding electrodes described hereinproduce welding fumes including levels of manganese that are less thancertain conventional gas-shielded flux cored welding electrodes. Themanganese content in certain non-limiting embodiments of gas-shieldedflux cored welding electrodes according to the present disclosure meetscertain Metal Fabrication Hazardous Air Pollutants (MFHAP) requirementsunder U.S. Environmental Protection Agency regulations at 40 CFR Part 63Subpart XXXXXX pertaining to alloying element content. In particular,EPA Subpart XXXXXX requires the electrode alloy content, based on totalelectrode weight, to be no greater than 1.0 weight percent manganese,0.1 weight percent nickel, 0.1 weight percent chromium, 0.1 weightpercent cadmium, and 0.1 weight percent lead.

Although it is known that manganese enhances certain weld metalproperties, it is also considered a hazardous component of the weldingfumes emitted from arc welding processes if inhaled above the levelsestablished by certain health and safety organizations. Reducingmanganese content in conventional gas-shielded flux cored electrodes canreduce the manganese level in the welding fumes. For example, FIG. 1shows the weight percentage manganese in welding fumes as a function ofelectrode manganese content in a 1/16-inch diameter E71T-9M flux coredwelding electrode during gas-shielded arc welding using a 75% Ar/25% CO₂shielding gas. However, reducing manganese content in a flux coredwelding electrode also can reduce manganese content in the weld metaland, in turn, weld metal toughness, tensile, and ductility properties.FIG. 2 shows the weight percentage manganese in weld deposits as afunction of welding electrode manganese content when the deposits wereformed using a 1/16-inch diameter E71T-9M flux cored welding electrodeduring gas-shielded arc welding using a 75% Ar/25% CO₂ shielding gas. Itwill be seen from FIG. 2 that weld deposit manganese content increaseswith increasing levels of manganese in the welding electrode. FIG. 3shows the relationship between yield strength (YS) and ultimate tensilestrength (UTS) of weld deposits as a function of welding electrodemanganese content when the deposits were formed using a 1/16-inchdiameter E71T-9M flux cored welding electrode during gas-shielded arcwelding using a 75% Ar/25% CO₂ shielding gas. In FIG. 3, both YS and UTSof the weld deposits decreased with a reduction in electrode manganesecontent. FIG. 4 shows the relationship between Charpy v-notch (CVN)impact toughness (evaluated at −20° F.) of weld deposits as a functionof welding electrode manganese content when the deposits were formedusing a 1/16-inch diameter E71T-9M flux cored welding electrode duringgas-shielded arc welding using a 75% Ar/25% CO₂ shielding gas. In FIG.4, CVN impact toughness of the weld deposits decreased with decreasingelectrode manganese content.

Thus, welding electrode design must address competing concerns, andreducing manganese content in flux cored welding electrodes to addresswelding fume manganese levels may impair weld deposit mechanicalproperties. Previously, there were no commercially availablegas-shielded flux cored welding electrodes that met the EPA SubpartXXXXXX 1.0% manganese maximum and 0.1% nickel maximum requirements,while also satisfying weld metal toughness, tensile, and ductilityproperties of AWS A5.20/A5.20M classifications E7XT-1C, E7XT-1M,E7XT-9C, E7XT-9M, E7XT-12C, and E7XT-12M.

Certain non-limiting embodiments of gas-shielded flux cored weldingelectrodes according to the present disclosure include lower manganeselevels than commercially available gas-shielded flux cored weldingelectrodes and thereby produce welding fumes including up to about 90%less manganese. Nevertheless, welding electrode embodiments according tothe present disclosure still satisfy weld metal toughness, tensile, andductility properties specified in AWS A5.20/A5.20M and AWS A5.36/A5.36M.Gas-shielded flux cored welding electrodes according to the presentdisclosure comprise a ferrous metal sheath and core ingredients enclosedwith the ferrous metal sheath. The gas-shielded flux cored electrodeshave the following composition, in weight percentages based on the totalweight of the sheath and core ingredients: 0.25 to 1.50 manganese; 0.02to 0.12 carbon; 0.003 to 0.02 boron; 0.2 to 1.5 silicon; 0 to 0.3molybdenum; at least one of titanium, magnesium, and aluminum, whereinthe combined content of titanium, magnesium, and aluminum is 0.2 to 2.5;remainder iron and incidental impurities. Optimizing the combination ofcarbon, boron, silicon, molybdenum and titanium, magnesium, and/oraluminum contents can allow for a substantial reduction in manganesecontent of the welding electrodes relative to commercially availablegas-shielded flux cored welding electrodes, while maintaining acceptableweld metal toughness, tensile, and ductility properties. The sheathencloses a particulate mixture of fluxing and possibly otheringredients.

Unless otherwise stated herein, the concentrations provided herein forthe various ingredients of flux cored welding electrodes according tothe present disclosure are in weight percentages calculated based on thecombined weight of the ferrous sheath and the core ingredients of thewelding electrode.

The gas-shielded flux cored electrodes according to the presentdisclosure may be fabricated using any conventional method ofmanufacturing such electrodes. In one non-limiting method ofmanufacturing welding electrodes according to the present disclosure, acoiled ferrous sheet steel is slit into strips. The strips are passedthrough rollers that form the strips into channels having a generallyU-shaped cross-section. In the same operation, the formed strip isfilled with a measured amount of particulate core ingredients. TheU-shaped strip is then passed through closing rolls, forming the stripinto a tube in which the core ingredients are enclosed. The tube is thendrawn, rolled, or swaged to a desired size smaller than the originaldiameter of the formed tube, thereby providing a final weldingelectrode. The final electrode may be baked to remove residuallubricants and moisture or used in the unbaked condition, depending onthe reduction process employed to manufacture the electrode. Othermethods for making welding electrodes according to the presentdisclosure will be apparent to those having ordinary skill upon considerthe present description.

After fabrication, gas-shielded flux cored electrodes according to thepresent disclosure may be used in a flux cored arc welding (FCAW)process wherein the shielding gas is selected from, for example, argon,carbon dioxide, oxygen, other inert gases, and mixtures of two or morethereof. Any FCAW equipment and process that incorporates a suitablepower source, wire (electrode) feeder, gun, and system for supplyingshielding gas can be used to weld materials using the gas-shielded fluxcored welding electrodes according to the present disclosure.

According to one aspect of the present disclosure, a gas-shielded fluxcored welding electrode includes a ferrous sheath enclosing particulatecore ingredients. The gas-shielded flux cored welding electrodecomprises, in weight percentages: 0.25 to 1.50 manganese; 0.02 to 0.12carbon; 0.003 to 0.02 boron; 0.2 to 1.5 silicon; 0 to 0.3 molybdenum; atleast one of titanium, magnesium, and aluminum, wherein the totalcontent of titanium, magnesium, and aluminum is 0.2 to 2.5; remainderiron and incidental impurities. The core ingredients include a fluxsystem comprising, in weight percentages: 3 to 12 titanium dioxide; 0.05to 1.0 of arc stabilizers; and less than 10% of other flux ingredients.The arc stabilizers may be, for example and without limitation, one ormore compounds of sodium oxide, potassium oxide, and/or other known arcstabilizers used in flux cored welding electrodes. The other fluxingredients may be, for example and without limitation, one or more ofsilicon dioxide, aluminum oxide, magnesium oxide, manganese oxide,zirconium oxide, and fluoride-containing compounds.

The flux system of the gas-shielded flux cored welding electrodesaccording to the present disclosure is based on titanium dioxide. TheTiO₂ content in the electrodes herein may be in the range of 3 to 12weight percent, and in certain embodiments is in the range of 7.0 to11.0 weight percent. The TiO₂ may be present in the pure rutile form,but also may be present in other forms suitable as a flux ingredient forgas-shielded flux cored welding electrodes. Non-limiting examples ofother suitable forms of TiO₂, which are also referred to herein as“TiO₂,” include alkali metal titanates, anatase, and leucoxene. The TiO₂component of the flux system helps to provide a slag viscosity andmelting point necessary to support the molten metal during welding,especially during welding in positions other than horizontal and flatpositions. TiO₂ also helps to stabilize the arc as the molten dropletscross from the electrode tip to the weld metal during welding.

The flux system of the gas-shielded flux cored welding electrodesaccording to the present disclosure includes one or more compounds ofsodium (Na) and/or other arc stabilizing compounds. The total weight ofthe one or more arc stabilizing compounds is in the range of 0.05 to 1.0weight percent, and in certain embodiments is in the range of 0.10 to0.60 weight percent, expressed as Na₂O. The arc stabilizing component ofthe flux system serves as an arc stabilizer and reduces spattergeneration during welding. The arc stabilizing component may include oneor more suitable compounds of Na, potassium (K), and lithium (Li), butalso may consist of or include other suitable arc stabilizers known inthe art. Examples of suitable arc stabilizers include compounds ofsodium oxide and potassium oxide.

Other possible components of the flux system of the gas-shielded fluxcored welding electrodes according to the present disclosure mayinclude, for example, one or more of silicon dioxide, aluminum oxide,magnesium oxide, manganese oxide, zirconium oxide, andfluoride-containing compounds that help control the slag's viscosityand/or melting point, improve weld bead fluidity and shape, help reduceweld metal diffusible hydrogen levels, and/or improve other weldingperformance characteristics. The total concentration of these othercomponents should be no more than 10 weight percent based on the totalweight of the sheath and core ingredients. In one embodiment, the othercomponents of the flux system include 0.10 to 0.80 weight percentsilicon dioxide, based on the total weight of the sheath and coreingredients.

The ferrous sheath and the core ingredients of the flux cored weldingelectrodes according to the present disclosure include one or morealloying ingredients intended to improve characteristics of the weldmetal. For example, and without limitation, the alloying ingredients maybe or include one or more of manganese, carbon, boron, silicon,molybdenum, titanium, magnesium, and aluminum. These alloying elementsmay be present in the ferrous strip as elements alloyed into the ferrousstrip material and/or may be present as a component of the coreingredients in, for example, pure metallic form and/or as part of one ormore ferroalloys. In any case, the alloying ingredients are present in aform that may readily be incorporated into the weld metal as alloyingelements.

Manganese may be present in the flux cored welding electrodes accordingto the present disclosure in a concentration of 0.25 to 1.50 weightpercent. Manganese is included in the electrodes to increase weld metaltoughness, tensile, and ductility properties. Manganese may alsofunction to assist in deoxidizing the weld pool during solidificationand thereby helps to inhibit weld metal porosity defects. In certainnon-limiting embodiments of flux cored welding electrodes according tothe present disclosure, manganese is present in the range of 0.50 to1.25 weight percent, and in certain embodiments is present in the rangeof 0.50 to 1.0 weight percent. The 0.25 to 1.50 weight percent manganeserange is lower than the manganese content of certain conventionalcommercially available gas-shielded flux cored electrodes, and thereduced manganese content of the electrodes may reduce manganese presentin the welding fumes by up to about 90%. Also, welding electrodeembodiments according to the present disclosure including no more than1.0 weight percent manganese satisfy the limit under Metal FabricationHazardous Air Pollutants (MFHAP) requirements under U.S. EnvironmentalProtection Agency regulations at 40 CFR Part 63 Subpart XXXXXX.

Carbon may be present in the flux cored welding electrodes according tothe present disclosure in the range of 0.02 to 0.12 weight percent, andin certain embodiments is present in the range of 0.03 to 0.10 weightpercent. Carbon may improve weld metal toughness, tensile, and ductilityproperties and in the electrodes according to the present disclosure,serves as a partial substitute for manganese in improving thoseproperties. Carbon also may be used to deoxidize the weld pool duringsolidification to help prevent weld metal porosity defects.

Boron may be present in the flux cored welding electrodes according tothe present disclosure in the range of 0.003 to 0.02 weight percent, andin certain embodiments is present in the range of 0.005 to 0.015 weightpercent. Boron may help to increase weld metal toughness properties andin the electrodes according to the present disclosure, serves as apartial substitute for manganese in that respect.

Silicon may be present in the flux cored welding electrodes according tothe present disclosure in the range of 0.2 to 1.5 weight percent, and incertain embodiments is present in the range of 0.3 to 1.0 weightpercent. Silicon may deoxidize the weld pool during solidification tohelp prevent weld metal porosity defects. Silicon also may affect thefluidity of the weld bead and increases the slag's viscosity and supportof the weld metal during solidification.

Molybdenum may be present in the flux cored welding electrodes accordingto the present disclosure in a concentration up to 0.3%. Molybdenum mayhelp to increase weld metal tensile properties. In certain weldingelectrode embodiments herein, molybdenum is absent.

One or more of titanium, magnesium, and aluminum may be present in theflux cored welding electrodes according to the present disclosure,including in both or either of the core and the sheath of theelectrodes, in quantities that are distinct from the quantities of suchmaterials that may be present in the flux of the electrodes. The totalconcentration of titanium, magnesium, and aluminum is 0.2 to 2.5 weightpercent. In certain non-limiting embodiments of a welding electrodeaccording to the present disclosure, the total content of titanium andmagnesium is in the range of 0.3 to 2.0 weight percent. Certain othernon-limiting embodiments include magnesium in the range of 0.4 to 1.0weight percent. In other embodiments, magnesium is present in the rangeof 0.2 to 1.0 weight percent, along with titanium additions in the rangeof 0.2 to 1.5 weight percent. Titanium, magnesium, and/or aluminumadditions may act as deoxidizers and may improve weld metal toughness,tensile, and ductility properties, and one or more of titanium,magnesium, and aluminum may be added to the electrodes according to thepresent disclosure as partial substitutes for manganese.

Conventional gas-shielded flux cored electrodes of the AWS A5.20 and AWSA5.36/A5.36M classifications E7XT-1C, E7XT-1M, E7XT-9C, E7XT-9M,E7XT-12C, and E7XT-12M including titanium dioxide based slag systemsutilize significant concentrations of manganese and may also use smallconcentrations of boron to achieve acceptable weld metal toughness,tensile, and ductility properties. However, these conventionalelectrodes also produce welding fumes during the welding process thatinclude significant levels of manganese. No commercially availablegas-shielded flux cored welding electrodes within these AWS A5.20 andAWS A5.36/A5.36M classifications meet the Metal Fabrication HazardousAir Pollutants (MFHAP) requirement under U.S. Environmental ProtectionAgency 40 CFR Part 63 Subpart XXXXXX.

As discussed above, FIG. 1 shows the relationship between electrodemanganese content and the manganese content of welding fumes generatedduring gas-shielded arc welding using the electrodes. Welding fume testswere conducted using procedures defined in AWS F1:2:2006, “LaboratoryMethod for Measuring Fume Generation Rates and Total Fume Emission ofWelding and Allied Processes”, the entire disclosure of which isincorporated herein. The average current and voltage used were 300 A and28V, respectively. It will be seen from FIG. 1 that the manganesecontent of welding fumes decreased significantly as the electrodemanganese content was reduced from conventional levels of about 2.2weight percent with all other major variables held constant. Thereduction in fume manganese content was up to 90% when the electrodemanganese content was reduced from the typical 2.25 weight percent levelto 0.25 weight percent.

As discussed above, FIG. 2 shows the relationship between electrodemanganese content and manganese content in the weld deposit duringgas-shielded arc welding using the electrodes. These tests wereconducted using AWS A5.20/A5.20M procedures with an average current andvoltage of 315 A and 28V, respectively. The weld metal manganese levelsdecreased as the manganese content in the electrode decreased. With allother major variables held constant, a reduction in manganese content ofthe electrode would reduce weld metal manganese content, therebyimpairing those useful mechanical and other properties of the weld metalenhanced by the presence of manganese.

As discussed above, FIG. 3 shows the relationship between electrodemanganese content and the yield and tensile properties of weld metaldeposits. These tests were conducted using AWS A5.20/A5.20M procedureswith an average current and voltage of 315 A and 28V, respectively.Manganese generally increases yield and tensile properties, all othervariables being held constant, and a significant reduction in both YSand UTS is seen to occur as manganese content is reduced from aconventional level of at least about 2.2 weight percent to levels lessthan 1.5 weight percent.

As discussed above, FIG. 4 shows the relationship between electrodemanganese content and CVN toughness properties of weld metal depositsformed using the electrodes. The tests were conducted using AWSA5.20/A5.20M procedures with an average current and voltage of 315 A and28V, respectively. Manganese generally improves weld metal toughnessproperties, and FIG. 4 shows that CVN toughness was significantlyimpaired when electrode manganese content was reduced from conventionallevels, all other variables being held constant.

FIG. 5 shows the relationship between fume generation rate (FGR) and themanganese content of the electrode during gas-shielded arc welding. FIG.5 indicates no major effects on FGR as electrode manganese content isreduced from conventional levels of at least about 2.2 weight percentwith all other major variables being held constant.

The following examples of low-manganese welding electrodes within thescope of the present disclosure show that the exemplary electrodes didnot exhibit any significant reduction in weld metal tensile and CVNtoughness properties as would be expected when significantly reducingelectrode manganese content from a typical range of 2.0 to 2.5 weightpercent down to the range of 0.25 to 1.50 weight percent. All testresults were obtained using AWS A5.20/A5.20M procedures, with theexception that ten CVN specimens, instead of the normal five specimens,were tested and averaged to show comparisons of electrode results. Insome cases, tests were repeated and the average results are shown in thefigures and tables. The AWS A5.20 mechanical property requirements varyslightly with the gas-shielded flux cored electrode classifications. AnE71T-9M FCAW electrode type was used to demonstrate the presentinvention using a 75% Ar/25% CO₂ shielding gas. The CVN toughness testswere conducted at −20° F., at which the minimum requirement foracceptable AWS A5.20 results is 20 ft-lbs. The required yield strengthis 58 ksi minimum, and the ultimate tensile strength required range is70 to 95 ksi.

As shown in FIGS. 3 and 4, the tensile properties (yield strength andultimate tensile strength) and CVN impact toughness are substantiallyreduced when manganese is reduced in a conventional flux coredelectrode. To determine the effects of carbon and boron additions for agas-shielded flux cored welding electrode including a low manganesecontent of 1.25 weight percent, a conventional electrode (“STD”) andthree experimental electrodes were evaluated. The data are shown inTable 1.

TABLE 1 STD #1 (Avg.) (Avg.) #2 #3 C 0.028 0.036 0.072 0.072 Mn 2.151.25 1.25 1.25 Si 0.58 0.59 0.59 0.59 B 0.0072 0.0072 0.0072 0.0144 Mg0.56 0.56 0.56 0.56 YS (ksi) 75.9 69.3 70.0 72.1 UTS (ksi) 83.2 77.579.9 81.6 % EL 28 30 31 28 CVN @ 81 33 75 84 −20° F. (Avg. ft-lbs)

Experimental electrode #1 included increased carbon and reducedmanganese relative to the conventional electrode. The test results forelectrode #1 showed a 59% reduction in CVN toughness compared to theconventional electrode, which contained a manganese content in theconventional range. Increasing carbon from 0.036 weight percent inelectrode #1 to 0.072 weight percent in experimental electrode #2 morethan doubled CVN toughness, while retaining a low manganese content of1.25 weight percent. In experimental electrode #3, carbon content wasincreased to 0.072 weight percent and boron content was increased from0.0072 weight percent to 0.0144 weight percent. These modificationfurther increased CVN toughness by 12% over electrode #2. The CVNtoughness of low manganese electrodes #2 and #3 were substantiallyequivalent to the CVN toughness of the conventional electrode containing2.15 weight percent manganese. Increasing both carbon and boron contentsin electrode #3 also increased YS and UTS to levels near those of theconventional electrode.

To determine the effects of carbon at a low electrode manganese contentof 0.90 weight percent, four additional experimental electrodeformulations were evaluated, and the data are provided in Table 2. TheCVN toughness of electrode #4, which included 0.028 weight percentcarbon, did not meet the AWS A5.20 minimum of 20 ft-lbs at −20° F.Increasing carbon content to a level above 0.07 weight percent inexperimental electrodes #5, #6, and #7 produced acceptable AWS A5.20 CVNtoughness values, with an optimum found around 0.08 weight percentcarbon. As carbon content was increased in electrodes #4 through #7, thetensile properties also trended upwardly to levels near those of theconventional electrode listed in Table 1.

TABLE 2 #6 #4 #5 (Avg.) #7 C 0.028 0.072 0.082 0.098 Mn 0.90 0.90 0.900.90 Si 0.59 0.59 0.59 0.59 B 0.0072 0.0072 0.0072 0.0072 Mg 0.56 0.560.56 0.56 YS (ksi) 67.9 67.1 68.7 70.8 UTS (ksi) 76.5 77.3 77.0 82.0 %EL 28 29 30 28 CVN @ 8 31 61 26 −20° F. (Avg. ft-lbs)

The effects of titanium and magnesium additions were investigated usinga series of experimental electrodes including a low manganese content of0.90 weight percent and 0.08 weight percent carbon. The results areshown in Table 3. Experimental electrodes #9 and #10 included 0.24 and0.47 weight percent titanium, respectively, and each electrode included0.56 weight percent magnesium. The CVN toughness values of electrodes #9and #10 were at least about equivalent to the toughness of the evaluatedconventional electrode including 2.15 weight percent manganese. Alllisted tensile properties in Table 3 for experimental electrodes #8, #9,and #10 meet AWS A5.20 requirements, and the tensile results fromelectrode #10 approximated those of the conventional electrode.

TABLE 3 STD #8 #10 (Avg.) (Avg.) #9 (Avg.) C 0.028 0.082 0.082 0.082 Mn2.15 0.90 0.90 0.90 Si 0.58 0.59 0.59 0.59 B 0.0072 0.0072 0.0072 0.0072Mg 0.56 0.56 0.56 0.56 Ti — — 0.24 0.47 Mg + Ti 0.56 0.56 0.80 1.03 YS(ksi) 75.9 68.7 66.8 71.8 UTS (ksi) 83.2 77.0 75.6 80.7 % EL 28 30 27 29CVN @ 81 61 97 79 −20° F. (Avg. ft-lbs)

The effects of a titanium addition with magnesium also were investigatedin a series of electrodes containing a very low manganese content of0.25 weight percent and a low carbon content of 0.036 weight percent.The results are shown in Table 4. The addition of 0.78 weight percenttitanium in experimental electrode #12 increased CVN toughness byapproximately 70% over electrode #11. A small increase in tensileproperties also was achieved with this titanium addition.

TABLE 4 #11 #12 C 0.036 0.036 Mn 0.25 0.25 Si 0.06 0.06 B 0.0072 0.0072Mg 0.58 0.58 Ti 0.00 0.78 Mg + Ti 0.58 1.36 YS (ksi) 61.9 63.3 UTS (ksi)70.7 73.0 % EL 28 28 CVN @ 7 57 −20° F. (Avg. ft-lbs)

To evaluate the effects of carbon at a low manganese content of 0.90weight percent and total titanium and magnesium content of 1.03 weightpercent, experimental electrodes were evaluated as shown in Table 5. TheCVN toughness increased as carbon was increased to approximately the0.06 to 0.08 weight percent range in electrodes #13, #14, and #10, andthe results were equivalent to the conventional electrode containing ahigh 2.15 weight percent manganese content. A corresponding increase intensile properties also occurred as carbon was increased toapproximately 0.11 weight percent in this series of experiments, and thetensile properties were similar to those of the conventional electrodeevaluated. All of these tests results met the AWS A5.20 requirements.

TABLE 5 STD (Avg.) #13 #14 #10 (Avg.) #15 C 0.028 0.056 0.066 0.0820.106 Mn 2.15 0.90 0.90 0.90 0.90 Si 0.58 0.59 0.59 0.59 0.59 B 0.00720.0072 0.0072 0.0072 0.0072 Mg + Ti 0.56 1.03 1.03 1.03 1.03 YS (ksi)75.9 68.4 66.6 71.8 72.7 UTS (ksi) 83.2 79.1 78.2 80.7 83.1 % EL 28 2929 29 28 CVN @ 81 50 82 79 23 −20° F. (Avg. ft-lbs)

Considering the above results from testing on experimental electrodeformulations, the present inventors identified various improvedlow-manganese gas-shielded flux cored electrode formulations. Onenon-limiting embodiment a gas-shielded flux cored electrode according tothe present disclosure includes a ferrous metal sheath and a core withinthe sheath enclosing particulate core ingredients, wherein the coreingredients and the sheath together include the following, in weightpercentages based on the total weight of the sheath and the coreingredients: 0.25 to 1.50 manganese; 0.02 to 0.12 carbon; 0.003 to 0.02boron; 0.2 to 1.5 silicon; 0 to 0.3 molybdenum; at least one oftitanium, magnesium, and aluminum, wherein the total content oftitanium, magnesium, and aluminum is 0.2 to 2.5; 3 to 12 titaniumdioxide; at least one arc stabilizer, where the total content of arcstabilizers is 0.05 to 1.0; no greater than 10 of additional flux systemcomponents; remainder iron and incidental impurities. In certainnon-limiting embodiments, the arc stabilizer includes at least one ofsodium oxide and potassium oxide compounds. In certain non-limitingembodiments, the additional flux system components include one or moreof silicon dioxide, aluminum oxide, magnesium oxide, manganese oxide,zirconium oxide, and fluoride-containing compounds.

An additional non-limiting embodiment of a gas-shielded flux coredelectrode according to the present disclosure includes a ferrous metalsheath and a core within the sheath enclosing particulate coreingredients, wherein the core ingredients and the sheath togetherinclude the following, in weight percentages based on the total weightof the sheath and the core ingredients: 0.50 to 1.25 manganese; 0.03 to0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; at least one oftitanium and magnesium, wherein the total content of titanium andmagnesium is 0.3 to 2.0; 7 to 11 titanium dioxide; 0.10 to 0.60 sodiumoxide; 0.10 to 0.80 silicon dioxide; remainder iron and incidentalimpurities.

A further non-limiting embodiment of a gas-shielded flux cored weldingelectrode according to the present disclosure includes a ferrous metalsheath and a core within the sheath enclosing particulate coreingredients, wherein the core ingredients and the sheath togetherinclude the following, in weight percentages based on the total weightof the sheath and the core ingredients: 0.50 to 1.25 manganese; 0.03 to0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.4 to 1.0magnesium; 7 to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to0.80 silicon dioxide; remainder iron and incidental impurities.

Yet a further non-limiting embodiment of a gas-shielded flux coredwelding electrode according to the present disclosure includes a ferrousmetal sheath and a core within the sheath enclosing particulate coreingredients, wherein the core ingredients and the sheath togetherinclude the following, in weight percentages based on the total weightof the sheath and the core ingredients: 0.50 to 1.25 manganese; 0.03 to0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.2 to 1.0magnesium; 0.2 to 1.5 titanium; 7 to 11 titanium dioxide; 0.10 to 0.60sodium oxide; 0.10 to 0.80 silicon dioxide; remainder iron andincidental impurities.

Yet another non-limiting embodiment of a gas-shielded flux cored weldingelectrode according to the present disclosure includes a ferrous metalsheath and a core within the sheath enclosing particulate coreingredients, wherein the core ingredients and the sheath togetherinclude the following, in weight percentages based on the total weightof the sheath and the core ingredients: 0.25 to 1.0 manganese; 0.03 to0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; at least one oftitanium and magnesium, wherein the total content of titanium andmagnesium is 0.3 to 2.0; 7 to 11 titanium dioxide; 0.10 to 0.60 sodiumoxide; 0.10 to 0.80 silicon dioxide; remainder iron and incidentalimpurities.

A further non-limiting embodiment of a gas-shielded flux cored weldingelectrode according to the present disclosure includes a ferrous metalsheath and a core within the sheath enclosing particulate coreingredients, wherein the core ingredients and the sheath togetherinclude the following in weight percentages, based on the total weightof the sheath and the core ingredients: 0.25 to 1.0 manganese; 0.03 to0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.4 to 1.0magnesium; 7 to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to0.80 silicon dioxide; remainder iron and incidental impurities.

An additional embodiment of a gas-shielded flux cored welding electrodeaccording to the present disclosure includes a ferrous metal sheath anda core within the sheath enclosing particulate core ingredients, whereinthe core ingredients and the sheath together include the following inweight percentages based on the total weight of the sheath and the coreingredients: 0.25 to 1.0 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015boron; 0.3 to 1.0 silicon; 0.2 to 1.0 magnesium; 0.2 to 1.5 titanium; 7to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicondioxide; remainder iron and incidental impurities.

In certain embodiments, the ferrous metal sheath of the gas-shieldedflux cored welding electrode according to the present disclosure isgenerally tubular. The gas-shielded flux cored welding electrodesaccording to the present disclosure may be adapted for use in flux coredarc welding wherein the shielding gas is selected from, for example,argon, carbon dioxide, oxygen, other inert gases, and mixtures of atleast two thereof.

This specification has been written with reference to variousnon-limiting and non-exhaustive embodiments. However, it will berecognized by persons having ordinary skill in the art that varioussubstitutions, modifications, or combinations of any of the disclosedembodiments (or portions thereof) may be made within the scope of thisspecification. Thus, it is contemplated and understood that thisspecification supports additional embodiments not expressly set forthherein. Such embodiments may be obtained, for example, by combining,modifying, or reorganizing any of the disclosed steps, components,elements, features, aspects, characteristics, limitations, and the like,of the various non-limiting embodiments described in this specification.

1. A gas-shielded flux cored welding electrode for use in comprising aferrous metal sheath and a core within the sheath including coreingredients, the core ingredients and the sheath together comprising, inweight percentages based on the total weight of the core ingredients andthe sheath: 0.25 to 1.50 manganese; 0.02 to 0.12 carbon; 0.003 to 0.02boron; 0.2 to 1.5 silicon; 0 to 0.3 molybdenum; at least one oftitanium, magnesium, and aluminum, wherein the total content oftitanium, magnesium, and aluminum is 0.2 to 2.5; 3 to 12 titaniumdioxide; at least one arc stabilizer, where the total content of arcstabilizers is 0.05 to 1.0; no greater than 10 of additional flux systemcomponents; iron; and incidental impurities.
 2. The gas-shielded fluxcored welding electrode recited in claim 1, wherein the ferrous metalsheath is generally tubular.
 3. The gas-shielded flux cored weldingelectrode recited in claim 1, wherein the electrode is adapted for usein flux cored arc welding wherein the shielding gas is selected fromargon, carbon dioxide, oxygen, other inert gases, and mixtures of atleast two thereof.
 4. The gas-shielded flux cored welding electroderecited in claim 1, where the at least one arc stabilizer comprises amaterial selected from compounds of sodium oxide and potassium oxide. 5.The gas-shielded flux cored welding electrode recited in claim 1,wherein the additional flux system components comprise at least one ofsilicon dioxide, aluminum oxide, magnesium oxide, manganese oxide,zirconium oxide, and fluoride-containing compounds.
 6. The gas-shieldedflux cored welding electrode recited in claim 1, wherein the coreingredients and the sheath together comprise, in weight percentagesbased on the total weight of the core ingredients and the sheath: 0.50to 1.25 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0silicon; at least one of titanium and magnesium, wherein the totalcontent of titanium and magnesium is 0.3 to 2.0; 7 to 11 titaniumdioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicon dioxide; iron;and incidental impurities.
 7. The gas-shielded flux cored weldingelectrode recited in claim 1, wherein the core ingredients and thesheath together comprise, in weight percentages based on the totalweight of the core ingredients and the sheath: 0.50 to 1.25 manganese;0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.4 to1.0 magnesium; 7 to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10to 0.80 silicon dioxide; iron; and incidental impurities.
 8. Thegas-shielded flux cored welding electrode recited in claim 1, whereinthe core ingredients and the sheath together comprise, in weightpercentages based on the total weight of the core ingredients and thesheath: 0.50 to 1.25 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015boron; 0.3 to 1.0 silicon; 0.2 to 1.0 magnesium; 0.2 to 1.5 titanium; 7to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicondioxide; iron; and incidental impurities.
 9. The gas-shielded flux coredwelding electrode recited in claim 1, wherein the core ingredients andthe sheath together comprise, in weight percentages based on the totalweight of the core ingredients and the sheath: 0.25 to 1.0 manganese;0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; at leastone of titanium and magnesium, wherein the total content of titanium andmagnesium is 0.3 to 2.0; 7 to 11 titanium dioxide; 0.10 to 0.60 sodiumoxide; 0.10 to 0.80 silicon dioxide; iron; and incidental impurities.10. The gas-shielded flux cored welding electrode recited in claim 1,wherein the core ingredients and the sheath together comprise, in weightpercentages based on the total weight of the core ingredients and thesheath: 0.25 to 1.0 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015boron; 0.3 to 1.0 silicon; 0.4 to 1.0 magnesium; 7 to 11 titaniumdioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicon dioxide; iron;and incidental impurities.
 11. The gas-shielded flux cored weldingelectrode recited in claim 1, wherein the core ingredients and thesheath together comprise, in weight percentages based on the totalweight of the core ingredients and the sheath: 0.25 to 1.0 manganese;0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.2 to1.0 magnesium; 0.2 to 1.5 titanium; 7 to 11 titanium dioxide; 0.10 to0.60 sodium oxide; 0.10 to 0.80 silicon dioxide; iron; and incidentalimpurities.
 12. A welding electrode comprising a metal sheath and a corewithin the sheath, the core and the sheath together comprising, inweight percentages based on the total weight of the core and the sheath:0.25 to 1.50 manganese; 0.02 to 0.12 carbon; 0.003 to 0.02 boron; 0.2 to1.5 silicon; 0 to 0.3 molybdenum; at least one of titanium, magnesium,and aluminum, wherein the total content of titanium, magnesium, andaluminum is 0.2 to 2.5; 3 to 12 titanium dioxide; at least one arcstabilizer, where the total content of arc stabilizers is 0.05 to 1.0;no greater than 10 of additional flux system components; iron; andincidental impurities.
 13. The welding electrode recited in claim 12,where the at least one arc stabilizer comprises a material selected fromcompounds of sodium oxide and potassium oxide.
 14. The welding electroderecited in claim 12, wherein the additional flux system componentscomprise at least one of silicon dioxide, aluminum oxide, magnesiumoxide, manganese oxide, zirconium oxide, and fluoride-containingcompounds.
 15. The welding electrode recited in claim 12, wherein thecore and the sheath together comprise, in weight percentages based onthe total weight of the core and the sheath: 0.50 to 1.25 manganese;0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; at leastone of titanium and magnesium, wherein the total content of titanium andmagnesium is 0.3 to 2.0; 7 to 11 titanium dioxide; 0.10 to 0.60 sodiumoxide; 0.10 to 0.80 silicon dioxide; iron; and incidental impurities.16. The welding electrode recited in claim 12, wherein the core and thesheath together comprise, in weight percentages based on the totalweight of the core and the sheath: 0.50 to 1.25 manganese; 0.03 to 0.10carbon; 0.005 to 0.015 boron; 0.3 to 1.0 silicon; 0.4 to 1.0 magnesium;7 to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80silicon dioxide; iron; and incidental impurities.
 17. The weldingelectrode recited in claim 12, wherein the core and the sheath togethercomprise, in weight percentages based on the total weight of the coreand the sheath: 0.50 to 1.25 manganese; 0.03 to 0.10 carbon; 0.005 to0.015 boron; 0.3 to 1.0 silicon; 0.2 to 1.0 magnesium; 0.2 to 1.5titanium; 7 to 11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to0.80 silicon dioxide; iron; and incidental impurities.
 18. The weldingelectrode recited in claim 12, wherein the core and the sheath togethercomprise, in weight percentages based on the total weight of the coreand the sheath: 0.25 to 1.0 manganese; 0.03 to 0.10 carbon; 0.005 to0.015 boron; 0.3 to 1.0 silicon; at least one of titanium and magnesium,wherein the total content of titanium and magnesium is 0.3 to 2.0; 7 to11 titanium dioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicondioxide; iron; and incidental impurities.
 19. The welding electroderecited in claim 12, wherein the core and the sheath together comprise,in weight percentages based on the total weight of the core and thesheath: 0.25 to 1.0 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015boron; 0.3 to 1.0 silicon; 0.4 to 1.0 magnesium; 7 to 11 titaniumdioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicon dioxide; iron;and incidental impurities.
 20. The welding electrode recited in claim12, wherein the core and the sheath together comprise, in weightpercentages based on the total weight of the core and the sheath: 0.25to 1.0 manganese; 0.03 to 0.10 carbon; 0.005 to 0.015 boron; 0.3 to 1.0silicon; 0.2 to 1.0 magnesium; 0.2 to 1.5 titanium; 7 to 11 titaniumdioxide; 0.10 to 0.60 sodium oxide; 0.10 to 0.80 silicon dioxide; iron;and incidental impurities.